Pressure store

ABSTRACT

A pressure store comprising sub-chambers ( 8, 54, 28 ) arranged in a housing ( 2 ), a first sub-chamber ( 8 ) arranged between the housing ( 2 ) and a flexible separating diaphragm ( 40 ), a second sub-chamber ( 54 ) arranged between the separating diaphragm ( 40 ) and a supporting body ( 48 ), and a third sub-chamber ( 28 ) encompassed by the supporting body ( 48 ), wherein the first sub-chamber ( 8 ) can be filled with a first fluid, wherein the second sub-chamber ( 54 ) and the third sub-chamber ( 28 ) are connected to one another in fluid-conducting fashion and can be filled with a second fluid, and wherein the first and the second sub-chamber ( 8, 54 ) vary in terms of their respective sizes as a result of movements of the separating diaphragm ( 40 ) as a function of the respective filling state, is characterized in that the first fluid is a storage medium and the second fluid is a working medium, and in that the second sub-chamber ( 54 ) is increased in size during the extraction of storage medium from the pressure store and is reduced in size during the filling of the pressure store with storage medium.

The invention relates to a pressure store comprising compartmentsarranged in a housing, a first compartment which is arranged between thehousing and a flexible separating diaphragm, a second compartment whichis arranged between the separating diaphragm and a support body, and athird compartment encompassed by the support body, with the firstcompartment being fillable with a first fluid, the second compartmentand the third compartment being connected to one another to conductfluid and being fillable with a second fluid, and the first and thesecond compartment varying in their respective size as a result ofmovements of the separating diaphragm as a function of the respectivefilling state.

Such an accumulator is known from DE 101 13 415 A1. In the knownaccumulator in the form of a hydropneumatic accumulator, there is aflexible separating element in an accumulator housing, formed by the endpiece of a pipe, and the element surrounds a support body which hasfluid passages. The support body, at least in individual sections, has anonround cross-sectional shape. The separating element is anchored onthe accumulator housing with the formation of a seal such that, on theoutside and inside of the separating element, receiving spaces areformed which are separate from one another. A centrally located throughbore forms a passage which leads to the inner receiving space of theaccumulator for a storage medium. There is a gas valve for filling theoutside gas space. The known accumulator can be used for energy storage,for example, in conjunction with vehicle suspension systems, or also aspulsation dampers. Furthermore, the known solution is especially wellsuited for damping of pressure peaks in hydraulic or otherfluid-engineering systems. The known solution leaves much to be desiredfor use as an accumulator for storage media in the form of chemicallycorrosive fluids, such as a urea-water solution.

Another accumulator is known from DE 38 10 509 C2. An accumulator isknown comprising a main body of a tank with an outer pipe of cylindricalshape on whose one end there is a side plate and on whose other endthere is a cover, at least one inlet opening and one outlet openingwhich are formed on the outer pipe, and a bladder or diaphragm forsubdividing the interior of the main body of the tank into a gas chamberand a liquid chamber, with an opening of the bladder being sealed tightby the cover. An insert is arranged such that it projects into thebladder for the purpose of reducing the volume of the gas chamber. Theinsert is formed from a base part, a middle part, and a head part, withthe head part being kept in contact with the bottom of the diaphragm;this makes it possible to prevent damage of the diaphragm by repeatedcontraction. In the contracted state, the bladder or diaphragm adjoinsthe insert.

Accumulators of this type are widely used in different sizes andstructural configurations in order to receive and discharge variablevolumes of pertinent fluids which are under the operating pressure of afluid system that is connected on the fluid side, with the bladder,which is under a preloading pressure of the working gas, forming apressure cushion on its gas side. The operational reliability of theaccumulator depends primarily on the accumulator bladder, whichtypically consists of a plastic material, especially butyl, whichbladder is exposed not only to mechanical stresses in operation, but isalso to be resistant to chemically corrosive storage fluids, ifpossible. As has been shown, in conjunction with corrosive fluids suchas urea-water solutions, it has so far not been possible to ensure aproblem-free service life of sufficient length for continuous operation,for example, over 20,000 hours.

So-called “urea injection” is being increasingly used in automotiveengineering in order to reduce the nitrogen oxide (NOx) emissions byinjection into the exhaust gas flow. In this type of application, it isespecially important that a long service life can be achieved withoutproblems in continuous operation.

In this respect, the object of the invention is to provide anaccumulator which is characterized by improved operational reliabilityin connection with corrosive storage media and which is thereforesuitable especially for use in urea injection in automotive engineering.

This object is achieved according to the invention by an accumulatorhaving the features specified in claim 1 in its entirety.

According to the characterizing part of claim 1, one important featureof the invention consists in that the first fluid is a storage mediumand the second fluid is a working medium and that the second compartmentis enlarged when the storage medium is removed from the accumulator andreduced in size when the accumulator is filled with the storage medium.The amount of the working medium to be accommodated is defined by thevolumes of the second and third compartment. When the first compartmentis filled with the storage medium, the flexible separating diaphragm ismoved such that the second compartment, which adjoins the thirdcompartment outside the support body, is reduced in size. Accordingly,the second compartment is enlarged when the storage medium is removedfrom the first compartment or when the filling of the latter with thestorage medium decreases.

Advantageously, the accumulator is designed as a hydropneumatic bladderaccumulator for a gaseous working medium and/or a liquid storage medium.Especially preferably, the accumulator is designed for filling of astorage medium in the form of a chemically corrosive fluid such as aurea-water solution. This affords the possibility of using theaccumulator according to the invention in urea injection, especially inthe automotive domain.

In one special configuration of the accumulator according to theinvention, the support body and the separating diaphragm are shaped anddimensioned such that at a volumetric size of the first compartmentwhich exceeds a definable boundary value, in other words, at avolumetric size which exceeds a maximum value for the storage mediumwhich is to be accommodated, the support body forms a support for theseparating diaphragm.

Furthermore, it is advantageous if the housing and the separatingdiaphragm are shaped and dimensioned such that the separating diaphragmat least partially adjoins the housing when the first compartment iscompletely emptied. Alternatively, the separating diaphragm can beshaped and dimensioned such that it is spaced apart from the supportbody and from the housing when the first compartment is completelyemptied.

The support body and the housing thus form an effective protection forthe separating diaphragm against overstress at excess pressures in thefirst and second compartment by the separating diaphragm or theaccumulator bladder being able to rest against the support body and thehousing and thus being protected against being crushed at excesspressures. The reduced mechanical loading leads to a prolongation of thesafe service life of the separating diaphragm even if it is exposed tochemically corrosive media such as a urea-water solution.

Typically, the housing has a head part which forms the closure of thehousing and which borders the second and/or third compartment. Thehousing is advantageously made cup-shaped, with the first compartmentbeing arranged on the bottom. In the head part, there can be aconnection device for the second fluid.

Furthermore, it is advantageous if on the head part there is a retainingbody on which the opening edge of the separating diaphragm is anchored.The retaining body preferably forms a retaining part on which thesupport body is arranged. This yields an especially compact constructionof the accumulator.

In one special configuration of the accumulator according to theinvention, the retaining body has the shape of a bell whose jacketsurrounds a fourth compartment which borders the third compartment. Inthis way, the intake capacity of the accumulator for the second fluid orthe typically gaseous working medium is enlarged, and, at the same time,the material demand for forming the accumulator is reduced.

In especially advantageous exemplary embodiments, the support body hasthe shape of a body of revolution which is made rounded and closed onthe end facing the first compartment and is provided with at least onelateral wall opening as a passage site between the second and thirdcompartment. In this configuration, the support body for the separatingdiaphragm or accumulator bladder can form a large-area support so thatthe accumulator bladder, which has essentially no folds at excesspressures, is optimally protected.

With respect to the configuration of the head part, the arrangement canbe advantageously made such that the head part has a cover part whichcan be screwed to the housing with inside wall parts in the form of aspherical cap which is concentric to the axis of the housing, and thatwithin the cover part the retaining body is arranged such that betweenits outside wall in the form of spherical surface parts and the insidewall parts of the cover part, a gap is formed for accommodating an edgeregion of the separating diaphragm which borders the opening edge.

Especially reliable anchoring of the separating diaphragm can beachieved when the retaining body in a region which is axially offsetfrom its retaining part in the direction of the connection device has anannular groove which has been machined into the outside wall and whichis engaged by an edge bead which surrounds the opening edge of theseparating diaphragm for the anchoring of the separating diaphragm.

In especially advantageous exemplary embodiments, the connection devicehas a screw fitting which extends through an opening of the cover partwhich is concentric to the central axis, which fitting pulls theretaining body against the inside wall of the cover part by screwing tothe cover part and clamps the edge region of the separating diaphragmlocated in the gap.

Especially advantageously, the arrangement can be made such that theretaining body in the region of the retaining part forms a circularcylinder on whose edge region catch elements are formed which withcounter-elements on the support body form a snap connection whichanchors the latter. This type of anchoring of the support body isespecially easy to mount and makes possible low production costs.

The catch elements on the outer wall of the retaining part can be offsetfrom its end edge and can be formed by depressions of the outer wall ofthe retaining part into which a bead-like projection which protrudesradially to the inside, can be snapped on the inside of the supportbody.

Alternatively, the catch elements on the inside wall of the retainingpart can be formed by a depression which is axially at a distance fromits end edge and a projection which adjoins the end edge and whichprotrudes radially to the inside, and said catch elements can be latchedto counter-elements by catch fingers which are distributed over theperiphery of the opening of the support body. In a collar of individualcatch fingers which has been formed in this way, mounting is madeespecially simple and convenient. The corresponding applies to exemplaryembodiments in which latching takes place on the outside of theretaining part. In this case, there can also be individual catch fingerson the end edge of the support body.

The support body is preferably formed from a plastic material.Especially advantageously in this case, it can be glass fiber-reinforcedpolyarylamide IXEF®, a material which, compared to conventional glassfiber-reinforced plastics, is characterized by a smooth, closed outerskin. Due to these properties, the retaining body and/or the connectiondevice can also be advantageously formed from this material.

The invention is detailed below using the drawings.

FIG. 1 shows a longitudinal section of one exemplary embodiment of theaccumulator according to the invention which is shown only slightlyenlarged compared to a practical embodiment;

FIG. 2 shows a longitudinal section of only one retaining body with thesupport body fixed thereon for the exemplary embodiment from FIG. 1;

FIG. 3 shows an extract of the region designated as III in FIG. 2,greatly enlarged compared to FIG. 2, and

FIG. 4 shows a longitudinal section which is similar to FIG. 2 and inwhich a modified example of the latching of the support body on theretaining body is shown.

The invention is explained below using the example of the use of theaccumulator for a urea injection system. In FIG. 1, which shows theexemplary embodiment of the accumulator as a whole, an accumulatorhousing is designated as 2 and for the most part has the shape of acircularly cylindrical cup on whose closed bottom 4 a throughflowopening 6 is located. The opening 6 which is aligned to the centrallongitudinal axis 10 enables supply and discharge of a first fluid, suchas a urea-water solution, to or from the first compartment 8 which islocated in the housing 2 bordering the bottom 4. A head part 12, whichcan be screwed to the accumulator housing 2, forms the fluid-tightclosure of the upper open end of the housing 2.

The head part 12 has an outer cover part 14 on which the screw couplingto the housing 2 is formed and which can consist of a metallic material,for example, of aluminum, as can also be the case for the housing 2.Alternatively, the cover part 14 can also be formed from a structurallystrong plastic material. The cover part 14 has a central opening 16which is concentric to the axis 10. At a short distance from the opening16, the cover part 14 has inner wall parts in the form of a sphericalcap 18 which is concentric to the axis 10. Within the cover part 14, thehead part 12 has a retaining body 20 with a screw fitting 22 which formsthe connection device for the second fluid, which is located integrallyon the retaining body, which extends through the opening 16 of the coverpart 14, and by means of which the retaining body 20 is fixed within thecover part 14 in interaction with a nut 24. A central fluid channel 26extends through the screw fitting 22 in order to fill a thirdcompartment 28 with the working medium which is under a preloadingpressure as the second fluid. A valve insert which is arranged withinthe channel 26 is not shown in the drawing.

The retaining body 20 has the shape of a bell whose jacket surrounds afourth compartment 30 which borders the third compartment 28. The belljacket on its outside wall forms spherical surface parts 34 which definebetween themselves and the spherical cap 18 of the cover part 14 aclamping gap 36 for the anchoring region 38 of a separating diaphragm40, which region is arranged in the gap 36. The bladder, which is formedfrom a plastic such as butyl, which is suitable for these types ofaccumulators, forms the flexible separating diaphragm 40 between thefirst compartment 28 and the second compartment 54. The retaining body20 between the end of the outer spherical surface part 34 and the screwfitting 22 has an annular groove 42 which for especially reliableanchoring of the separating diaphragm 40 engages an edge bead 44 whichsurrounds its opening edge.

The retaining body 20 with the bell located within the bladder formed bythe separating diaphragm 40 forms a retaining part 46 for the anchoringof a support body 48 which projects into the interior of the bladder.The support body is formed from a relatively structurally strong plasticmaterial, with glass fiber-reinforced polyarylamide IXEF® having provenitself especially well suited. As FIG. 1 shows, the support body 48 hasthe shape of a body of revolution with a spherically rounded, closedlower end located at a distance from the bottom 4 of the housing 2 andsurrounds a third compartment 28 which borders the fourth compartment30. The other upper end 50 of the support body 48 is fixed on theretaining part 46 by means of a snap connection. As FIG. 1 moreovershows, the support body 48 in a longitudinal section is somewhatV-shaped and has side wall openings 52 for the passage of the workingfluid to the second compartment 54, which borders the third compartment28.

The details of the snap connection are best illustrated in FIGS. 2 and3. As is apparent, at a short distance from the end edge 56 of theretaining part 46, depressions 56 and 60 are formed in which the endregion of the support body 48 can be accommodated, and a projection 62of the support body 48 which protrudes radially to the inside can besnapped into the depression 60. The retaining body 20 in this example,in the same manner as the support body 48 and the valve located in thechannel 26 of the fitting 22, is formed from glass fiber-reinforcedpolyarylamide IXEF®, so that the retaining body 20 with the support body48 fixed thereon forms a unit which consists completely of plastic.

In operation, when used for urea injection, the first compartment 8 ofthe accumulator is filled with the urea-water solution by means of apump until an upper value of the system pressure of the system pressureis reached and the pump shuts off. The storage medium for meteredinjection is forced into the system by the accumulator pressure. When alower pressure value is reached, the pump starts again. If unwantedexcess pressures should occur and a certain boundary value of the volumeincrease of the first compartment 8 is exceeded, the separatingdiaphragm 40 rests against the support body 48 and is thus protectedagainst overload and damage.

FIG. 4 shows one version of the configuration of the snap connection,with the catch elements now being arranged on the inner wall of theretaining part 46 of the retaining body 20. As FIG. 4 shows, it is adepression 64 which is axially at a distance from the end edge 56, and aprojection 66 which adjoins the end edge 56 and which protrudes radiallyto the inside. The counter-elements on the side of the support body 48are formed by retaining fingers 68 which are arranged distributed overthe periphery of the opening of the support body 48. Forcounter-elements formed by individual catch fingers 68, theestablishment of the latching is made especially simple and convenient.

In the embodiment of the latching shown in FIGS. 2 and 3, on the outsideof the retaining part 46 of the retaining body 20, the counter-elementsof the support body 48 could also be formed from individual,peripherally distributed catch fingers.

1. A pressure store comprising compartments (8, 54, 28) arranged in ahousing (2), a first compartment (8) which is arranged between thehousing (2) and a flexible separating diaphragm (40), a secondcompartment (54) which is arranged between the separating diaphragm (40)and a support body (48), and a third compartment (28) encompassed by thesupport body (48), with the first compartment (8) being fillable with afirst fluid, the second compartment (54) and the third compartment (28)being connected to one another to conduct fluid and being fillable witha second fluid, and the first and the second compartment (8, 54) varyingin their respective size as a result of movements of the separatingdiaphragm (40) as a function of the respective filling state,characterized in that the first fluid is a storage medium and the secondfluid is a working medium, and that the second compartment (54) isenlarged when the storage medium is removed from the pressure store andreduced in size when the pressure store is filled with the storagemedium.
 2. The accumulator according to claim 1, characterized in thatthe accumulator is made as a hydropneumatic bladder accumulator for agaseous working medium and/or a liquid storage medium.
 3. Theaccumulator according to claim 1, characterized in that the accumulatoris made for filling of a storage medium in the form of a chemicallycorrosive fluid such as a urea-water solution.
 4. The accumulatoraccording to claim 1, characterized in that the support body (48) andthe separating diaphragm (40) are shaped and dimensioned such that thesupport body (48) at a volumetric size of the first compartment (8)which exceeds a definable boundary value forms a support for theseparating diaphragm (40).
 5. The accumulator according to claim 1,characterized in that the housing (2) and the separating diaphragm (40)are shaped and dimensioned such that the separating diaphragm (40) atleast partially adjoins the housing (2) when the first compartment (8)is completely emptied.
 6. The accumulator according to claim 1,characterized in that the separating diaphragm (40) is shaped anddimensioned such that it is spaced apart from the support body (48) andfrom the housing (2) when the first compartment (8) is completelyemptied.
 7. The accumulator according to claim 1, characterized in thatthe housing (2) has a head part (12) which forms the closure of thehousing (2) and which borders the second and/or third compartment (54,28).
 8. The accumulator according to claim 7, characterized in that inthe head part (12) there is a connection device (22) for the secondfluid.
 9. The accumulator according to claim 7, characterized in that onthe head part (12) there is a retaining body (20) on which the openingedge of the separating diaphragm (40) is anchored.
 10. The accumulatoraccording to claim 9, characterized in that the retaining body (20)forms a retaining part (46) on which the support body (48) is arranged.11. The accumulator according to claim 9, characterized in that theretaining body (20) has the shape of a bell whose jacket surrounds afourth compartment (30) which borders the third compartment (28). 12.The accumulator according to claim 1, characterized in that the supportbody (48) is a body of revolution which is made rounded and closed onthe end facing the first compartment (8) and is provided with at leastone wall opening (52) as a passage site between the second compartment(54) and third compartment (28).
 13. The accumulator according to claim9, characterized in that the head part (12) has a cover part (14) whichcan be screwed to the housing (2) with inside wall parts in the form ofa spherical cap (18) which is concentric to the axis (10) of the housing(2), and that within the cover part (14) the retaining body (20) isarranged such that between its outside wall in the form of sphericalsurface parts (34) and the inside wall parts of the cover part (14), agap (36) is formed for accommodating an edge region (38) of theseparating diaphragm (40) which borders the opening edge.
 14. Theaccumulator according to claim 9, characterized in that the retainingbody (20) in a region which is axially offset from its retaining part(46) in the direction of the connection device (22) has an annulargroove (42) which has been machined into the outside wall and which isengaged by an edge bead (44) which surrounds the opening edge of theseparating diaphragm for the anchoring of the separating diaphragm (40).15. The accumulator according to claim 13, characterized in that theconnection device has a screw fitting (22) which extends through anopening (16) of the cover part (14) which is concentric to the centralaxis (10), which fitting pulls the retaining body (20) against theinside wall of the cover part (14) by screwing to the cover part (14)and clamps the edge region (38) of the separating diaphragm (40) locatedin the gap (36).
 16. The accumulator according to claim 10,characterized in that the retaining body (20) in the region of theretaining part (46) forms a circular cylinder on whose edge region catchelements (58, 60) are formed which with counter-elements (62) on thesupport body (48) form a snap connection which anchors the latter. 17.The accumulator according to claim 16, characterized in that the catchelements on the outer wall of the retaining part (46) are offset fromits end edge (56) and are formed by depressions (58, 60) of the outerwall of the retaining part (46) into which a bead-like projection (62)which protrudes radially to the inside can be snapped on the inside ofthe support body (48).
 18. The accumulator according to claim 16,characterized in that the catch elements on the inside wall of theretaining part (46) are formed by a depression (64) which is axially ata distance from its end edge (56) and a projection (66) which adjoinsthe end edge (56) and which protrudes radially to the inside, and saidcatch elements can be latched to counter-elements by catch fingers (68)which are distributed over the periphery of the opening of the supportbody (48).
 19. The accumulator according to claim 1, characterized inthat the support body (48) is formed from plastic, preferably from glassfiber-reinforced polyarylamide IXEF®.
 20. The accumulator according toclaims 9, characterized in that the retaining body (20) and/or theconnection device (22) is formed from plastic, especially from glassfiber-reinforced polyarylamide IXEF®.